Energy Conversion and Management 50 (2009) 21872199

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Energy Conversion and Managementjournal homepage: www.elsevier.com/locate/enconman

A review of heat-pump drying (HPD): Part 2 Applications and performance assessmentsNeslihan Colak a, Arif Hepbasli b,*a b

Department of Food Engineering, Faculty of Engineering, Pamukkale University, 20070 Denizli, Turkey Department of Mechanical Engineering, Faculty of Engineering, Ege University, 35100 Bornova, Izmir, Turkey

a r t i c l e

i n f o

a b s t r a c tIn the second part of this study, heat-pump drying systems were comprehensively reviewed in terms of applications and performance evaluations. In this regard, these systems were classied in terms of type of heat pump systems, type of dryer and product types rst. The performance assessments included coefcient of performance (COP), specic energy consumption (SEC) and specic moisture extraction rate (SMER), while types of energetic, exergetic and cost analyses were covered. It may be concluded that the most preferred method used to determine the HPD efciency is SMER, while in recent years exergetic analysis method has been widely used. 2009 Elsevier Ltd. All rights reserved.

Article history: Received 21 September 2008 Accepted 27 April 2009 Available online 2 June 2009 Keywords: Heat-pump dryer Energy Exergy Specic moisture extraction rate (SMER)

1. Introduction Drying has been used in a variety of industries, such as agricultural, chemical, timber, textile, paper, pharmaceuticals. The main objective of any drying process is to produce a dried product of desired quality at a minimum cost and maximum throughput by optimizing the design and operating conditions [1]. Drying is an energy-intensive operation consuming 925% of national energy in the developed countries [2]. Thus, to reduce energy consumption per unit of product moisture, it is necessary to scrutinize different methodologies to improve the energy efciency of the drying equipment [3]. Exergy analyses can reveal whether or not and by how much it is possible to design more efcient thermal systems by reducing the sources of existing inefciencies [4]. Exergy analysis has been applied successfully to various areas of engineering applications [5]. This paper is part 2 of the study on a review of heat-pump drying applications. Historical development, system descriptions and reviewing of HPD studies was given in part 1. In this part, classication of HPD systems was comprehensively given. 2. Classication of HPD applications 2.1. Type of heat pump systems Different types of HPs are available on the market for drying applications. In this study, HP types used for drying were reviewed under three main topics.* Corresponding author. Tel.: +90 232 388 400x5124 17; fax: +90 232 388 8562. E-mail address: arif.hepbasli@ege.edu.tr (A. Hepbasli). 0196-8904/$ - see front matter 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2009.04.037

2.1.1. Air source heat-pump drying systems As can be seen in Table 1, air source HP systems were mostly used in studies about HPD. Xanthopoulos et al. [6] presented the mathematical modeling of a single-layer drying of whole gs in an experimental HP of closed cycle. This system is showed schematically in Fig. 1. A prototype two-stage evaporator heat-pump-assisted mechanical drying system was designed, fabricated, and tested for enhancing heat recovery by Chua and Chou [7]. This two-stage HPD is presented in Fig. 2. 2.1.2. Ground source heat-pump drying systems Despite many studies about HPD systems have been done for a long years, ground source HPD studies are quite limited. Schematic illustration of a ground source HP drying system is illustrated in Fig. 3. This system consists of mainly three subsystems; (a) ground source heat exchanger (b) HP system, and (c) drying chamber. The main components of the HP system are an evaporator, a condenser, a compressor and an expansion valve. In this system, heat is extracted from the ground by the ground source heat exchanger, where a water-antifreeze solution is circulated. The heat is transferred to the refrigerant in the evaporator, upgraded in the HP cycle, and is supplied to the drying chamber. In here, heat is rejected to the drying air and this heated air enters the drying chamber [8]. 2.1.3. Chemical heat-pump drying systems A chemical HP (CHP) is proposed as one of the potentially signicant technologies for effective energy utilization in drying. The CHP can store thermal energy such as the waste heat from dryer exhaust, solar energy, geothermal energy, etc. in the form

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Nomenclature COP MER SMER SEC coefcient of performance (dimensionless) moisture extraction (evaporation) rate (kg moisture/ kWh) specic moisture extraction (evaporation) rate (kg moisture/kWh) specic energy consumption (kWh/kg moisture) Abbreviations HP heat pump HPD heat-pump dryer GEHP gas engine driven heat pump LAC lactic acid bacteria CHP chemical heat pump CHPD chemical heat-pump dryer

Table 1 Classication of heat-pump drying systems [7,8,17,2022,27,28,31,33,37,3942,44,45,47,52,54,58,6062,67,72,73,7579,81103]. Investigators Type of heat-pump dryer ASHP Geerarert [87] Hodgett [86] Oliver [89] Tai et al. [88] Zylla et al. [90] Cunney and Williams [91] Jolly et al. [31] Meyer and Greyvenstein [92] Rossi et al. [54] Birchall [93] Clements et al. [33] Jia at al. [17] Hesse [94] Birchall [95] Strommen and Kramer [37] Barneveld et al. [96] Strommen and Jonassen [22] Abrahamsson et al. [72] Bannister et al. [81] Hawlader et all. [84] Hawlader et all. [97] Prasertsan and Saen-saby [40,85] Schmidt et al. [75] Soponronnarit et al. [41] Achariyaviriya et al. [98] Ho et al. [52] Klocker et al. [76] Adapa et al. [58] Alves-Filho [99] Braun et al. [27] Hawlader et al. [100] Oktay [77] Oktay and Hepbasli [78] Sosle at al. [45,47] Teeboonma et al. [42] Ameen and Bari [79] Fernandez-Goln Seco et al. [82] Ogura et al. [73] Queiroz et al. [101] Zhang et al. [39] Adapa and Schoenau [28] Colak and Hepbasli [8] Chua and Chou [7] Fatouh et al. [60] Hawlader and Jahangeer [20] Soylemez [102] Ceylan et al. [44] Hancioglu and Hepbasli [61] Hancioglu and Hepbasli [62] Shi et al. [67] Hawlader et al. [21] Lostec et al. [83] Colak et al. [103] X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X GSHP CHP Dryers types FB B X X X X C Timber Textile, clay, timber Grain Grain Vegetables Ginger, potatoes Foam rubber Foam rubber, sliced carrots, root ginger Ginger, potatoes Granular food and biotechnological products Paper Timber Yam Sawn rubber wood, banana Laundry Papaya glace Papaya glace Potatoes Laundry Specialty crops Cranberry and potatoturnip mixtures Clothes Food grains Wool Wool Apple Papaya and mango glace Clothes Wood Ceramics Tomatoes Carrot cubes Specialty crops Apple Jews mallow, spearmint, parsley Green beans Timber Laurel leaves Laurel leaves Horse mackerel Wood chip Mint leaves Product Performance of systems SMER X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X COP SEC E X X X Ex Cost

X X X X X X X X X X X X X X X X X X X X X X

X X X X

SMER: specic moisture extraction rate, COP: coefcient of performance. SEC: specic energy consumption, E: energy analysis. Ex: exergy analysis, Cost: cost analysis.

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Air mix Evaporator

Drying cabinet

Expansion valve Compressor Fan

Resistance CondenserFig. 1. Closed cycle heat-pump dryer [6].

1 Fresh air intake air louver 2 Air damper 3 Economiser 1 4 High presure evaporator 5 Low pressure evaporator 6 Economiser 2 7 Centrifugal fan 8 Exhaust air louver 9 Hot gas condenser 10 Subcooler 1 11 Subcooler 2 12 Heating bank 13 Load-cell 14 Water tray 15 Data logger 16 Personal computerFig. 2. Schematic arrangement of the two-stage modular heat-pump dryer [7].

of chemical energy via an endothermic reaction in a suitably designed reactor and release the energy at various temperature levels during the heat-demand period by exo/endothermic reactions [9 12]. Ogura and Mujumdar [11] reported that the calcium oxide hydration/dehydration system was found to be the most feasible for CHPD systems from the viewpoints of temperature level, safety, corrosion and cost. Fig. 4 shows a schematic diagram of the CHP unit employed [12]. A CHPD system using the CAO/H2O/Ca(OH)2 reaction operating in the heat enhancement and refrigeration modes is presented in Fig. 5 [13]. Ogura et al. [12] presented an experimental study focusing on the heat and mass transfer performance in batch drying using the CHP.

Rolf and Corp [14] developed a CHPD for drying of bulky material such as bark and lumber. This method of drying is easy to adapt to any industrial drying process, but in particular the drying processes in the pulp and paper industry. 2.1.4. Hybrid heat-pump drying systems Some of the HPDs include hybrid sources, such as solar, microwave, infrared or conventional energy. The rst studies about combination of HPs and microwave drying were proposed in the literature by Lawton [15], and Metaxas and Meredith [16]. The feasibility and overall performance of this hybrid drying system was investigated by Jia et al. [17]. This study indicated that with the careful design of a HP assisted microwave drying has comparable to conventional convective drying in energy consumption. Schematic illustration of this system is shown in Fig. 6.

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Moist Air

Dryer

Drying Air

Condenser

Compressor Expansion Valve Evaporator

Refrigerant

Ground heat exchanger

Water + Antifreeze

Fig. 3. Schematic illustration of a ground source HPD [8].

Fig. 4. Schematic diagram of a CHP unit [12].

Zbicinski et al. [18] investigated convective air drying and infrared (IR) drying, while they suggested intermittent irradiation drying mode coupled with convective air drying for heat-sensitive materials. Marshall and Metaxas [19] combined a radio frequency (RF) heating with a conventional HP drying. A typical RF assisted HPD comprises a vapor compression HP system retro-tted with a RF generating system capable of imparting radio frequency energy to the drying material at various stage of the drying process. Hawlader and Jahangeer [20] built a fully equipped experimental solar assisted HP drying system set-up for drying

of green beans. This system is illustrated in Fig. 7 schematically. Hawlader et al. [21] found that the evaporatorcollector performed better than the air collector in a solar assisted heat-pump drying system. 2.2. Type of dryer Although batch shelf or tray dryers or kilns (for wood) are the most commonly used dryers in conjunction with HPs, other types may also be used (i.e., uidized beds [22,23], rotary dryers).

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Fig. 5. CHPD system using the CAO/H2O/Ca(OH)2 reaction [13].

Bypass air

Air damper

Expansion valve

Evaporator

Condenser

Water Hot air

Compressor Magnetrons Moist air Product inlet

Drying chamber

Product outletFig. 6. Schematic of a combined heat pump microwave dryer [17].

However, dryers that consume large amounts of drying air, e.g., ash or spray dryers, are not particularly suited for HP operation [24]. 2.2.1. Batch dryer HPD system more suitable for drying to batch operation than to continuous one because batch systems allow total recirculation with a very low air leakage rate, giving rise to high thermal efciencies [25]. An example of HP batch type dryer is showed in Fig. 8. Rahman et al. [26] used this system for measuring and modeling the desorption isotherm and HP air drying kinetics of peas.

The feasibility of an air HP cycle for tumbler clothes dryers was investigated by Braun et al. [27]. As can bee seen in Fig. 9, this type of dryer is an example of batch dryers. Tumbler dryers have been especially used for clothes drying. This dryer offered up to a 40% improvement in energy efciency over the electric dryer. 2.2.2. Conveyor dryer Continuous bed drying shows promising results over batch drying and can potentially be a better option for specialty crops. Very few studies have been done on HP assisted continuous bed dryers compared to HP assisted batch dryers [28].

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Fig. 7. A schematic of a solar assisted heat-pump drying system and water heater [20].

2

3

4

9 8 1

5 7

6Fig. 8. A schematic diagram of the heat pump dehumidier dryer [26] 1, Vapor-sealed and insulated structure; 2, humidier; 3, overheat vent; 4, external condenser; 5, heat pump dehumidier; 6, condensate; 7, product tray; 8, primary air circulation fan; 9, air distributor.

Strommen [29] developed a tunnel dryer for heat-sensitive products. A schematic illustration of this HP tunnel dryer is given in Fig. 10 [30]. Jolly et al. [31] developed a model for the continuous operation of an HPD that predicts the air conditions in the system; heat

transfer rate in the evaporator, condenser and external waste system; COP of the HPD and maximum efciency achievable. This model was used by Jia et al. [32] and by Clements et al. [33] to investigate the performance of a HP assisted continuous dryer.

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Fig. 9. A schematic of a closed air cycle heat pump tumbler dryer [27].

Electric energy Condenser 2 Compressor

Evaporator Condenser 1

Fan

TrolleysFig. 10. A schematic of a heat pump tunnel dryer [30].

Clements et al. [33] used wet foam rubber in a continuous bed dryer and showed that the SMER of the dryer doubled from 1.25 to 2.5 kg kWh1 when the relative humidity of the air at the dryer exit increased from 32% to 80%. Chou et al. [34] described an approach using the contact factor as the dryer performance and design parameter. In this study, they used the drying of agricultural products in a co-current continuous tunnel dryer as a reference case study. Unlike batch dryers, the continuous dryers are much easier to control since the energy ows and temperatures are constant, as the material is more uniform and ows through at a constant rate [28]. Because the construction of continuous drying systems may

require high engineering, modeling, and design costs, the benets need to be evaluated on the basis of cost rather than on energy efciency alone [35]. Adapa and Schoenau [28] designed, developed and validated a prototype HP continuous bed dryer, which can be used for commercial production and processing of specialty crops. Block diagram of this system is given in Fig. 11. 2.2.3. Fluidized bed dryer Fluidized bed drying (FBD) has been applied, to found many applications for drying of granular solids in the food, ceramic, pharmaceutical and agriculture industries [36]. Fluid-bed dryers can be

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Conveyor 1 Power input Compressor

Conveyor 2

Drying chamber Condenser Heat Pump Evaporator Condensate

Fig. 11. A block diagram of prototype heat pump conveyor dryer [28].

Fig. 12. A schematic of a uidized bed heat-pump dryer [35].

made simple and, combined with a HP system; they might be competitive in the food industry and the pharmaceutical industry [35]. Strommen and Kramer [37] studied about a low temperature dryer with a HP. The dryer was based on the uidized bed principle with the possibility of using air or inert gas as the drying medium. Strommen and Jonassen [22] and Alves-Filho and Strommen [23] described the development of novel, counter-current HP uidized bed dryers with high SMERs for the drying of heat-sensitive products. A uidized bed HP drying unit along with its components is given by Claussen et al. [35]. This system is shown in Fig. 12. Alves-Filho et al. [38] presented a simulation component model for a multiple uidized beds HPD with two independent drying

loops and two refrigerant circuits. The layout for modeling the multi-stage uid bed HPD is illustrated in Fig. 13. Zhang et al. [39] designed and constructed a HP assisted uidized bed dryer for drying of carrots cubes. 2.3. Product types HPDs have been used for drying of various products, such as fruits and vegetables, meat, paper, wood, timber, clothes, ceramics, chemical and biological materials. Studies about HP drying of various products were reviewed in this section. Preliminary studies indicated that the color and aroma qualities of dried agricultural products using HPs were better than those products using conventional hot-air dryers [37,4042].

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Evaporator Low temperature chamber

Evaporator

High temperature chamber

Throttling valve

Throttling valve T-head

Blower

Compressor Motor

Compressor Motor

M

M Condenser

3-way valve

3-way valve

T- headPump Condenser

Pump

Condenser

Fig. 13. Component model generated multi-stage uid bed heat-pump dryer plant [38].

One of the most popular industrial methods for drying of bananas is a HPD [43]. Prasertsan and Saen-Saby [40] found that, a saving of 44% of the running cost was achievable for the HPD implementation in banana drying. Chua et al. [3] studied about drying of banana slices in a two-stage HPD. Time-varying drying air temperature in batch drying of banana slices is shown to have favorable impact on drying kinetics as well as the color of the dried products. Ranjan et al. [43] presented a model which tested was validated with experimental data from different sources for stepwise drying of banana using a HPD as well as continuous batch dryer. Ceylan et al. [44] designed a HPD controlled PID for drying of kiwi, avocado and banana. Sosle et al. [45] found that the nal quality of the HP dried apple slices in terms of consumer preference was perfect. Perera [46] observed that modied atmosphere HP dried apples showed excellent color and retention of Vitamin C. Sosle et al. [47] demonstrated that a HPD could be successfully used for drying of apple. They also determined the performance of HPD for apple drying. Performance evaluation of the drying of apple slice in a GSHPD was made by Colak and Hepbasli [8] using exergy analysis method. Stawczyk et al. [48] designed and built a HP assisted atmospheric freeze dryer and investigated the drying effect on the quality of apple cubes compared with the result of convective and vacuum freeze-drying process. Vazquez et al. [49] described a pilot scale drying plant comprising a closed-circuit, hot air convection chamber with a HP and determined the kinetics of drying of grapes. Xanthopoulos et al. [6] presented the mathematical modeling of single-layer drying of whole gs in an experimental HP of closed cycle. Sunthonvit et al. [50] indicated that, a HPD was the best system for preservation of volatile compounds in sliced dried fruit followed by cabinet and tunnel dryer. Potato was used as a typical heat-sensitive material since its hygro-thermal properties. The percentage reductions in overall color change for HP dried potato were found to be 87% by Chua et al. [51]. Ho et al. [52] presented an optimization framework for drying of potato slice as a heat sensitive product in two-stage HPD. Sun et al. [1] used a batch HPD designed to permit simulta-

neous application of conduction and radiation heat for drying of potatoes. Hawlader et al. [53] studied about drying of potato, apple and guava in a HPD under inert environmental conditions and investigated the impact on color, surface porosity and rehydration abilities. Rectangular-shaped potato and apple slices as model composite food products were dried in a batch type HPD by Rahman et al. [26]. In this study, composite product showed better drying performance compared to single apple or potato samples. Rossi et al. [54] obtained an energy saving of about 30%, with better product quality for drying of onion slices in a HPD when compared with conventional dryers. Wood [55] examined quality of taste dried ginger at HPD. Results from this HP work indicated that volatile constituents had been retained in higher concentrations than those subjected to freeze-drying. Hot-air drying with partial air recirculation gave similar result to heat-pump drying. Chua and Chou [7] designed of a highly energy-efcient HP drying system with good air conditioning control mechanism to produce high quality dried agricultural and marine products. Rahman et al. [56] modeled the moisture desorption isotherm and thin layer drying kinetics of peas in a HPD. Adapa et al. [57] developed a simplied mathematical model of a HP assisted crop dryer and investigated the performance and veried its accuracy with respect to the experimental results [57,58]. Adapa and Schoenau [28] dried special crops such as ginseng, herbs and echinacea in a re-circulating HP continuous bed dryer system. Alves-Filho et al. [59] described experiments on atmospheric HP drying of red peppers. Fatouh et al. [60] investigated the drying characteristics of different herbs (Jews mallow, spearmint and parsley) using a dryer assisted by a HP to increase the dryer productivity and reduce the energy consumption. Hancioglu Kuzgunkaya and Hepbasli [61,62] evaluated performance analysis of GSHPD for drying of laurel leaves at two different temperatures. Newbert [63] found that, the energy consumption for drying of malt with a coupled gas engine HP (GEHP) dryer could be reduced by 40%. This system was presented in Fig. 14 [64].

Blower

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Exhaust air heat exchanger Air from malt kiln

Exhaust air to atmosphere Engine exhaust gas heat exchanger

Gas engine Gas in Evaporator

Exhaust gas

Compressor

Hot air to kiln V-1 Expansion valve Condenser

Pump

Gas engine radiator Condenser coil Fresh air Water/Glycol Refrigerant

Run-around coil heat exchanger

Fig. 14. Schematic illustration of gas engine heat-pump drying system [63,64].

Namsanguan et al. [65] showed that superheated steam dried (SSD) followed by a HP dried shrimp had much lower degree of shrinkage, higher degree of rehydration, better colors, less tough and softer, and more porous than single stage SSD shrimp. Nathakaranakule et al. [66] studied about different combined superheated-steam drying techniques for chicken meat. Drying characteristics of horse mackerel dried in a HP dehumidier were investigated by Shi et al. [67]. Cardona et al. [68] studied on HPDs as an alternative to freezedrying for dehydration of lactic acid bacteria for starter cultures. Alves-Filho et al. [69] suggested that two-stage heat-pump drying is an efcient and environmentally friendly technology while producing dried protein of high quality, enhanced properties, and reduced costs. Different applications of absorption HPs for paper drying were investigated by Friedel [70]. An open absorption HP conguration was used to dehumidify and reheat air streams for convection drying by Lazzarin and Longo [71]. Abrahamsson et al. [72] identied some waste heat streams, available in the paper drying process that can be used for energy recovery using different HP systems with special emphasis on both compression and absorption HPs.

Ogura et al. [73] estimated the potential of a new chemical HPD application to an industrial ceramics drying process from the viewpoints of energy and cost saving. Gopalnarayan et al. [74] described a simulation method for a closed loop HPD for clothes drying. Schmidt et al. [75] compared the thermodynamic behaviors of two dehumidication HP cycles: the subcritical R134A process and the transcritical CO2 process. Klocker et al. [76] designed and constructed a laboratory prototype laundry dryer using CO2 as working uid. This system was shown in Fig. 15 schematically. Braun et al. [27] reported the feasibility of an air HP cycle for a tumbler clothes dryer. Oktay [77] and Oktay and Hepbasli [78] investigated the performance of a HP assisted mechanical opener drying system for drying of wetted wool. Ameen and Bari [79] made the feasibility of using the condenser waste heat from a domestic air conditioner, hitherto rejected to the atmosphere, for clothes drying. This system is presented in Fig. 16. Dehumidifying HPs are mainly used for drying of timber and other heat-sensitive materials [79]. Modular HP dehumidiers, which are widely used in chamber-type wood-drying kilns, were designed to allow the dehumidier to be moved as required for

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Closed air circuit

Rotary drum

Gas cooler

Evaporator Fan Compressor

Auxiliary heat exchanger Expansion valveFig. 15. A heat-pump dryer prototype using carbon dioxide as working uid [76].

Heat pump circuit

Vent

Drying chamber

Ambient air

Condenser

T-X valve

Compresor

Evaporator

Ambient air

Space for coolingFig. 16. Simple integrated heat pump system for clothes drying [79].

Vent

operational exibility [80]. The performance of a HP dehumidier kiln was measured, and the kiln energy balance assessed, during commercial-scale drying of timber by Bannister et al. [81]. Electric-driven HP drying was evaluated in lumber from different softwoods and hardwoods by Fernandez-Goln Seco et al. [82]. Ceylan et al. [43] performed energy and exergy analyses of drying of poplar and pine timbers in a HPD. Lostec et al. [83] studied about thermal and economic analysis of drying of wood chip in absorption HPD.

3. Conclusions For development of sustainable energy, three important technological changes have been required: energy economies on the demand side, efciency improvements in the energy production, and renewing of fossil fuels by various sources of renewable energy. In this regard, HPD systems improve energy efciency and cause less fossil fuel consumption, so this system appropriate to sustainable development concept.

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N. Colak, A. Hepbasli / Energy Conversion and Management 50 (2009) 21872199 [25] Perera CO, Rahman MS. Heat pump demuhidier drying of food. Trends Food Sci Technol 1997;8:759. [26] Rahman MS, Perera CO, Thebaud C. Desorption isotherm and heat pump drying kinetics of peas. Food Res Int 1998;30(7):48591. [27] Braun JE, Bansal PK, Groll EA. Energy efciency analysis of air cycle heat pump dryers. Int J Refrig 2002;25:95465. [28] Adapa PK, Schoenau GJ. Re-circulating heat pump assisted continuous bed drying and energy analysis. Int J Energy Res 2005;29:96172. [29] Strommen I. Drying of heavily salted codsh. Ph.D. Thesis, The Norwegian Institute of Technology, Division of Refrigeration Engineering, Trondheim, Norway; 1980. [30] Kudra T, Mujumdar AS. Advanced drying technologies. New York: Marcel Dekker, Inc.; 2002. [31] Jolly P, Jia X, Clements S. Heat pump assisted continuous drying part 1: simulation model. Int J Energy Res 1990;14:75770. [32] Jia X, Jolly P, Clements S. Heat pump assisted continuous drying part 2: simulation results. Int J Energy Res 1990;14:77182. [33] Clements S, Jia X, Jolly P. Experimental verication of a heat pump assisted continuous dryer simulation model. Int J Energy Res 1993;17:1928. [34] Chou SK, Hawlader MNA, Ho JC, Chua KJ. The contact factor for dryer performance and design. Int J Energy Res 1999;23:127791. [35] Claussen IC, Ustad TS, Strommen I, Walde PM. Atmospheric freeze drying a review. Dry Technol 2007;25:95767. [36] Chua KJ, Mujumdar AS, Chou SK. Intermittent drying of bioproducts an overview. Bioresour Technol 2003;90:28595. [37] Strommen I, Kramer K. New applications of heat pumps in drying processes. Dry Technol 1994;12(4):889901. [38] Alves-Filho O, Thorbergen E, Strmmen I. A component model for simulation of multiple uidized bed heat pump dryers. In: Proceedings of the eleventh international drying symposium, vol. A; 1998. p. 94101. [39] Zhang X, Mao Z, Sun L. Heat pump uidized bed drying of agricultural materials. Annual meeting of American society of agricultural and biological engineers; 2004. [40] Prasertsan S, Saen-saby P. Heat pump drying of agricultural materials. Dry Technol 1998;16(1&2):23550. [41] Soponronnarit S, Nathakaranakule A, Wetchacama S, Swasdisevi T, Rukprang P. Fruit drying using heat pump. RERIC Int Energy J 1998;20:3953. [42] Teeboonma U, Tiansuwan J, Soponronnarit S. Optimization of heat pump fruit dryers. J Food Eng 2003;59:36977. [43] Ranjan R, Irudayaraj J, Reddy JN, Mujumdar AS. Finite-element simulation and validation of stepwise drying of bananas. Numer Heat Trans Part A 2004;45:9971012. [44] Ceylan I, Aktas M, Dogan H. Mathematical modeling of drying characteristics of tropical fruits. Appl Therm Eng 2007;27:19316. [45] Sosle VR, Raghavan GSV, Kittler R. Low temperature drying process for heat sensitive agri-food products. ASAE Annual International Meeting; 2000. [46] Perera CO. Modied atmosphere heat pump drying of food products. In: Proceedings of the second Asia-oceania drying conference; 2001. p. 46976. [47] Sosle V, Raghavan GSV, Kittler R. Low-temperature drying using a versatile heat pump dehumidier. Dry Technol 2003;21(3):53954. [48] Stawczyk J, Li S, Witrowa-Rajchert D, Fabisiak A. Kinetics of atmospheric freeze-drying of apple. Trans Porous Med 2007;66:15972. [49] Vazquez G, Chenlo F, Moreira R, Cruz E. Grape drying in a pilot plant with a heat pump. Dry Technol 1997;15:899920. [50] Sunthonvit N, Srzednicki G, Craske J. Effects of drying treatments on the composition of volatile compounds in dried nectarines. Dry Technol 2007;25:87781. [51] Chua KJ, Chou SK, Ho JC, Mujumdar AS, Hawlader MNA. Cyclic air temperature drying of guava pieces: effects on moisture and ascorbic acid contents. Trans Inst Chem Eng, Part C 2000;78:728. [52] Ho JC, Chou SK, Mujumdar AS, Hawlader MNA, Chua KJ. An optimization framework for drying of heat sensitive products. Appl Therm Eng 2001;21:177998. [53] Hawlader MNA, Perera CO, Tian M. Comparison of the retention of 6-gingerol in drying under modied atmosphere heat pump drying and other drying methods. Dry Technol 2006;24:516. [54] Rossi SJ, Neues LC, Kicokbusch TG. Thermodynamic and energetic evaluation of a heat pump applied to the drying of vegetables. In: Mujumdar AS, editor. Drying92. Elsevier Science; 1992. p. 14758. [55] Wood A. Flavor quality assessment of heat pump dried ginger. Seminar on the development and application of heat pump dryers, pacic power energy services; 1994. p. 4559. [56] Rahman SMA, Islam MR, Mujumdar AS. A study of coupled heat and mass transfer in composite food products during convective drying. Dry Technol 2007;25:135968. [57] Adapa PK, Schoenau GJ, Sokhansanj S. Performance study of a heat pump dryer system for specialty cropspart 2: model verication. Int J Energy Res 2002;26:102133. [58] Adapa PK, Schoenau GJ, Sokhansanj S. Performance study of a heat pump dryer system for specialty cropspart 1: development of a simulation model. Int J Energy Res 2002;26:100119. [59] Alves-Filho O, Eikevik T, Mulet A, Garau C, Rossello C. Kinetics and mass transfer during atmospheric freeze drying of red pepper. Dry Technol 2007;25:115561. [60] Fatouh M, Metwally MN, Helali AB, Shedid MH. Herbs drying using a heat pump dryer. Energy Convers Manage 2006;47:262943.

In this study, various HP drying systems were reviewed in more detail. The main conclusions, which may be drawn from the results of the present study, were listed below: a. Different types of HP drying systems are appropriate for drying of many products, especially heat sensitive products. b. Many researchers have found that the HPD uses energy more efciently compared with conventional drying systems. c. Quality of HP dried products has been found good. d. The widely used method for determining efciency of the HPD system is SMER. e. Studies on HPD have increased from day to day. f. Modied atmospheric and hybrid HPD studies have also signicantly increased in recent years because good quality foods have been requested gradually.

References[1] Sun L, Islam MR, Ho JC, Mujumdar AS. A diffusion model for drying of a heat sensitive solid under multiple heat input modes. Bioresour Technol 2005;96:155160. [2] Mujumdar AS. Handbook of industrial drying, vol. 2. New York, NY: Marcel Dekker Inc.; 1995. p. 124172. [3] Chua KJ, Mujumdar AS, Hawlader MNA, Chou SK, Ho JC. Batch drying of banana pieces effect of stepwise change in drying air temperature on drying kinetics and product color. Food Res Int 2001;34:72131. [4] Dincer I, Sahin AZ. A new model for thermodynamic analysis of a drying process. Int J Heat Mass Transfer 2004;47:64552. [5] Szargut J, Morris DR, Stewart FR. Exergy analysis of thermal, chemical and metallurgical Processes. New York: Taylor & Francis; 1988. [6] Xanthopoulos G, Oikonomou N, Lambrinos G. Applicability of a single layer drying model to predict the drying rate of whole gs. J Food Eng 2007;81:5539. [7] Chua KJ, Chou SK. A modular approach to study the performance of a twostage heat pump system for drying. Appl Therm Eng 2005;25:136379. [8] Colak N, Hepbasli A. Exergy analysis of drying of apple in a heat pump dryer. In: Second international conference of the food industries & nutrition division on future trends in food science and nutrition; 2005. p. 14558. [9] Goetz V, Elie F, Spinner B. The structure and performance of single effect solidgas chemical heat pumps. Heat Recov Syst CHP 1991;13(1):7996. [10] Mbaye M, Aidoun Z, Valkov V, Legault A. Analysis of chemical heat pumps (CHPS): basic concepts and numerical model description. Appl Therm Eng 1997;18(3):13846. [11] Ogura H, Mujumdar AS. Proposal for a novel chemical heat pump dryer. Dry Technol 2000;18(4&5):103353. [12] Ogura H, Yamamoto T, Kage H, Matsuno Y, Mujumdar AS. Effects of heat exchange condition on hot air production by a chemical heat pump dryer using CaO/H2O/Ca(OH)2 reaction. Chem Eng J 2002;86:310. [13] Ogura H, Yamamoto T, Otsubo Y, Ishida H, Kage H, Mujumdar AS. A control strategy for a chemical heat pump dryer. Dry Technol 2005;23: 11891203. [14] Rolf R, Corp R. Chemical heat pump for drying of bark. Annual meeting: technical section, Canadian pulp and paper association; 1990. p. 30711. [15] Lawton J. Drying: the role of heat pumps and electromagnetic elds. Phys Technol 1978;9:21420. [16] Metaxas AC, Meredith R. Industrial microwave heating. London: Peter Peregrinus Ltd.; 1983. [17] Jia X, Clements S, Jolly P. Study of heat pump assisted microwave drying. Dry Technol 1993;11(7):1583616. [18] Zbicinski I, Jakobsen A, Driscoll JL. Application of infra-red radiation for drying of particulate material. In: Mujumdar AS, editor. Drying92. Elsevier Science Publisher B.V.; 1992. p. 70411. [19] Marshall MG, Metaxas AC. Modeling the radio frequency electric eld strength developed during the RF assisted heat pump drying of particulates. Int Microwave Power Inst 1998;33(3):16777. [20] Hawlader MNA, Jahangeer KA. Solar heat pump drying and water heating in the tropics. Solar Energy 2006;80:4929. [21] Hawlader MNA, Rahman SMA, Jahangeer KA. Performance of evaporatorcollector and air collector in solar assisted heat pump dryer. Energy Convers Manage 2008;49:16129. [22] Strommen I, Jonassen O. Performance tests of a new 2-stage counter-current heat pump uidized bed dryer. In: Proceedings of the tenth international drying symposium; 1996. p. 5638. [23] Alves-Filho O, Strommen I. Performance and improvements in heat pump dryers. In: Proceedings of the tenth international drying symposium; 1996. p. 40516. [24] Chua KJ, Chou SK, Ho JC, Hawlader MNA. Heat pump drying: recent developments and future trends. Dry Technol 2002;20(8):1579610.

N. Colak, A. Hepbasli / Energy Conversion and Management 50 (2009) 21872199 [61] Hancioglu Kuzgunkaya E, Hepbasli A. Exergetic evaluation of drying of laurel leaves in a vertical ground-source heat pump drying cabinet. Int J Energy Res 2007;31:24558. [62] Hancioglu Kuzgunkaya E, Hepbasli A. Exergetic performance assessment of a ground source heat pump drying system. Int J Energy Res 2007;31:76077. [63] Newbert GJ. Energy efcient drying, evaporation and similar processes. J Heat Recov Syst 1985;5:5519. [64] Hepbasli A, Erbay Z, Icier F, Colak N, Hancioglu E. A review of gas engine driven heat pumps for residential and industrial applications. Renew Sustain Energy Rev 2009;13(1):8599. [65] Namsanguan Y, Tia W, Devahastin S, Soponronnarit S. Drying kinetics and quality of shrimp undergoing different two stage drying processes. Dry Technol 2004;22(4):75978. [66] Nathakaranakule A, Kraiwanichkul W, Soponronnarit S. Comparative study of different combined superheated-steam drying techniques for chicken meat. J Food Eng 2007;80:102330. [67] Shi QL, Xue CH, Zhao Y, Li ZJ, Wang XY. Drying characteristics of horse mackerel (Trachurus japonicus) dried in a heat pump dehumidier. J Food Eng 2008;84:1220. [68] Cardona TD, Driscoll RH, Paterson JL, Srzednicki GS, Kim WS. Optimizing conditions for heat pump dehydration of lactic acid bacteria. Dry Technol 2002;20(8):161132. [69] Alves-Filho O, Eikevik TM, Goncharova-Alves SV. Single- and multistage heat pump drying of protein. Dry Technol 2008;26:4705. [70] Friedel W. The large scale applications of heat pumps. In: Second international symposium, York, UK; 1984. [71] Lazzarin R, Longo G. Open cycle absorption heat pump for convection drying. IEA Heat Pump Centre Newslett 1994;12(4):225. [72] Abrahamsson K, Stenstrom S, Aly G, Jernqvist A. Application of heat pump systems for energy conservation in paper drying. Int J Energy Res 1997;21:63142. [73] Ogura H, Hamaguchi N, Kage H, Mujumdar AS. Energy and cost estimation for application of chemical heat pump dryer to industrial ceramics drying. Dry Technol 2004;22(1&2):30723. [74] Gopalnarayanan G, Radermacher R. Heat pump assisted dryer using refrigerant mixtures batch mode drying. ASHRAE Trans 1997;2:88895. [75] Schmidt EL, Klocker K, Flacke N, Steimle F. Applying the transcritical CO2 process to a drying heat pump. Int J Refrig 1998;21(3):20211. [76] Klocker K, Schmidt EL, Steimle F. Carbon dioxide as a working uid in drying heat pumps. Int J Refrig 2001;24:1007. [77] Oktay Z. Testing of a heat pump assisted mechanical opener dryer. Appl Therm Eng 2003;23:15362. [78] Oktay Z, Hepbasli A. Performance evaluation of a heat pump assisted mechanical opener dryer. Energy Convers Manage 2003;44:1193207. [79] Ameen A, Bari S. Investigation into the effectiveness of heat pump assisted clothes dryer for humid tropics. Energy Convers Manage 2004;45:1397405. [80] Carrington CG, Bannister P, Liu Q. Performance analysis of a dehumidier using HFC-134a. Int J Refrig 1995;18:47785. [81] Bannister P, Bansal B, Carrington CG, Sun ZF. Impact of kiln losses on a dehumidier dryer. Int J Energy Res 1998;22:51522. [82] Fernandez-Goln Seco JI, Fernandez-Goln Seco JJ, Hermoso Prieto E, Conde Garcia M. Evaluation at industrial scale of electric-driven heat pump dryers. Holz Roh Werkst 2004;62:2617. [83] Lostec BL, Galanis N, Baribeault J, Millette J. Wood chip drying with an absorption heat pump. Energy 2008;33:50012.

2199

[84] Hawlader MNA, Bong TY, Yang Y. A simulation and performance analysis of a heat pump batch dryer. In: Proceedings of the eleventh international drying symposium, vol. A; 1998. p. 20815. [85] Prasertsan S, Saen-saby P. Heat pump dryers: research and development needs and opportunities. Dry Technol 1998;16(1&2):25170. [86] Hodgett DL. Efcient drying using heat pump. Chem Eng 1976:510612. [87] Geeraert B. Air drying by heat pumps with special reference to timber drying. In: Camatini E, Kester T, editors. Heat pumps and their contribution to energy conservation. Leydon: Noordhoff; 1976. p. 21946. [88] Tai KW, Devotta S, Watson RA, Holland FA. The potential for heat pumps in drying and dehumidication systems III: an experimental assessment of the heat pump characteristics of a heat pump dehumidication system using R114. Int J Energy Res 1982;6:33340. [89] Oliver TN. Process drying with a dehumidifying heat pump. In: Proceedings international symposium on the industrial application of heat pumps; 1982. p. 7388. [90] Zylla R, Abbas P, Tai KW, Devotta S, Watson FA, Holland FA. The potential for heat pumps in drying and dehumidication systems I: theoretical considerations. Energy Res 1982;6:30522. [91] Cunney MB, Williams P. An engine-driven heat pump applied to grain drying and chilling. In: Proceedings second international symposium on the large scale applications of heat pumps; 1984. p. 28394. [92] Meyer JP, Greyvenstein GP. The drying of grain with heat pumps in South Africa: a techno-economic analysis. Int J Energy Res 1992;16:1320. [93] Birchall S. Heat pump drier-investigating energy efciency. In: Proceedings development and application of heat pump drier; 1993. [94] Hesse B. Heat pump driers: some basic principles, design considerations and energy efciency. Seminar on the development and application of heat pump dryers, pacic power energy services; 1994. p. 713. [95] Birchall S. Heat pump dryers investigating energy efciency. Seminar on the development and application of heat pump dryers, pacic power energy services; 1994. p. 2131. [96] Barneveld N, Bannister P, Carrington CG. Development of the ECNZ electric heat pump dehumidier drier pilot-plant. Annu Conf Inst Prof Eng NZ 1996;2(1):6871. [97] Hawlader MNA, Chou SK, Ho JC, Chua KJ. On the development of a heat pump dryer to maximize heat recovery. In: Proceedings of the eleventh international drying symposium, vol. A; 1998. p. 61623. [98] Achariyaviriya S, Soponronnarit S, Terdyothin A. Mathematical model development and simulation of heat pump fruit dryer. Dry Technol 2000;18(1&2):47991. [99] Alves-Filho O. Combined innovative heat pump drying technologies and new cold extrusion techniques for production of instant foods. Dry Technol 2002;20(8):154157. [100] Hawlader MNA, Chou SK, Jahangeer KA, Rahman SMA, Eugene Lau KW. Solar-assisted heat pump dryer and water heater. Appl Energy 2003;74: 18593. [101] Queiroz R, Gabas AL, Telis VRN. Drying kinetics of tomato by using electric resistance and heat pump dryers. Dry Technol 2004;22(7):160320. [102] Soylemez MS. Optimum heat pump in drying systems with waste heat recovery. J Food Eng 2006;74:2928. [103] Colak N, Kuzgunkaya E, Hepbasli A. Exergetic assessment of drying of mint leaves in a heat pump dryer. J Food Process Eng 2008;31:28198.